Permanent anisotropic magnet and method of making same



April 19, 1969 c. P. MARKS ET AL 2,933,427

PERMANENT ANISOTROPIC MAGNET AND METHOD OF MAKING SAME Filed March 15, 19s? 2 Sheets-Sheet 1 5 1 minutes FIGJ CurizTcmp.

minutes 10 FIG.2

IN VENTOR CHRISTIAAN PHILIP MARKS JOHANNES FLIPSE AGENT April 19, 1960 c. P. MARKS ETA!- 2,933,427

PERMANENT ANISOTROPIC MAGNET AND METHOD OF MAKING SAME Filed March 15, 1957 v 2 Sheets-Sheet 2 I. i 2 a 4 s 6 7 0 IO a2 minutes INVENTOR CHRISTIAAN PHILIP MARKS JOHANNES FLIPSfi BY M AGNT United States Patent T PERMANENT ANISOTROPIC MAGNET AND METHOD OF MAKING SAME Christiaan Philip Marks and Johannes Flipse, Eindhoven,

Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Application March 15, 1957, Serial No. 646,248 Claims priority, application Netherlands March 28, 1956 4 Claims. (Cl. 148-403) This invention relates to anisotropic permanent magnets and methods of making the same.

In particlular, the invention relates to permanent magnets consisting of ferrous alloys containing about 15 to 42% cobalt, about to 20% nickel, about 6 to 10% aluminium, about 2 to 8% of copper, about 4 to 10% titanium and the balance principally iron which have been subjected to special magnetic and thermal treatment to render the magnet anisotropic with (BH) values which are greater than those obtainable on similar alloys not subjected to this special treatment.

A thermal and magnetic treatment for such alloys is described in a copending application Serial No. 559,982, filed January 18, 1956, now Patent 2,837,452. In this treatment, the alloy is quenched from a temperature above 1200 to a temperature of about 900 C. and held at a temperature of about 10 to 70 C. below the Curie ice to said temperature below the Curie temperature.

In a preferred embodiment of the invention, the alloy contains between 28 and 42% of cobalt.

The invention will be described in connection with the accompanying drawing in which Fig. 1 is a curve of the cooling and magnetic hardening cycle of the method according to the invention,

Fig. 2 is a curve of a variation of the cycle shown in Fig. 1, and

Fig. 3 is a series of curves showing different cooling rates for different bodies.

As shown in Fig. 1, an alloy of the aforesaid type is initially at a temperature of about 1250 C. and is cooled by compressed air to about 600 C. in about two minutes in the presence of a magnetic field. The alloy is immediately reheated to about 820 C., in the presence of the magnetic field, and maintained at that temperature for about eight minutes, during which time the alloy magnetically hardens. Thereafter, the alloy is cooled to ambient temperatures.

point of the alloy for about 4 to 15 minutes, in a magnetic field. As a result of this thermal and magnetic treatment, the alloy becomes anisotropic and has a (BH). which is at least 700,000 gauss-oersted greater than that obtainable by more conventional thermal and magnetic treatments. However, this particular type of thermal and magnetic treatment is limited to bodies having relatively small dimensions, larger bodies not being readily quenched. More particularly, if large magnetic bodies were quenched in a medium such as water or the like in order to obtain a sufliciently rapid cooling, the bodies would be seriously damaged, and thus a medium such as compressed air should be used.

Accordingly, it is a principal object of the invention to provide a method of subjecting ferrous alloys of the aforesaid type to a thermal and magnetic treatment which is particularly advantageous for large bodies and which produces magnetically anisotropic bodies having a (BH) value exceeding by at least 700,000 gaussoersted, the (BH) obtainable by the aforesaid method.

Another object of this invention is to provide a moth od of making an anisotropic permanent magnet having a (BH) of at least 4.3 l0

These and other objects of the invention will appear as the specification progresses.

In accordance with the invention, a body of a ferrous alloy of the aforesaid type which is so large that it cannot be quenched in water or the like, is cooled from 1200 C. to 600 C. in more than one and less than ten minutes in the presence of a magnetic field after which it is heated, also in a magnetic field, from 600 C. to a temperature of about 10 to 70 C. below the Curie temperature of the alloy, and maintained at the latter temperature which varies not more than 20 C. for about 2 to 30 minutes while in the presence of the magnetic field.

Further, in accordance with the invention, after cooling to 600 C., the body may be cooled to ambient temperatures with or without the presence of a magnetic field and then reheated to said temperature below the Curie point in the presence of a magnetic field. Alternately the Alternatively, the alloy is initially cooled to ambient temperature (Fig. 2) in about five minutes, reheated to about 820 C. in about three minutes, the magnetic field being present while the alloy is cooling to 600 C. and also during reheating above 600 C. The alloy is then magnetically hardened for about ten minutes at 820 C. in the presence of a magnetic field and allowed to cool to ambient temperature.

A comparison of the cooling rates of various bodies is shown in Fig. 3. Curve 1 shows, for comparison, the rate of cooling required in the method described in the above-mentioned patent. This curve is rather steep since the body is cooled from above 1200 C. to about 600 C. in one minute or less. Because large bodies are difiicult to cool this rapidly, the technique according to our invention is preferred. The large bodies, instead of being quenched, are rapidly cooled by a blast of compressed air. As shown by curves 2, 3, 4 and 5, these bodies are cooled from above 1200 C. to about 600 C. in about 2 to 10 minutes.

The following table illustrates the improvement obtainable in accordance with the invention. Two bodies, one having dimensions 30 x 30 x 10 mms. and the other 20 X 30 x 50 mms. having the compositions indicated in col. 1 were subjected to one of the following treatments:

Method I The body was chilled to 600 C. in the time indicated in the heading of each of the last four columns of the table without the presence of a magnetic field, reheated to a temperature of about 800 C., and maintained at the latter temperature for about 10 minutes in the presence of a magnetic field. The last four columns indicate the (BI-D value obtained after the body is cooled to ambient temperature and magnetized in a magnetic field whose direction is substantially parallel to the direction of the field applied during the thermal treatment.

Method 11 The same as method I except that a magnetic field is applied while the body is cooled from above 1200" C. to 600 C. and reheated to the constant temperature below the Curie point. Because of the difiiculty in cooling a body of substantial dimension such as those of the aforesaid type from above 1200 C. to 600 C. in one minute, only a body having dimensions 30 X 30 x 10 mms. was prepared and subjected to the methods I and II containing 34% of Co with cooling from 1200 C. to 600 C. taking place in one minute.

Curie (BH)IJII\X; Cooled from 1,210 C-GOO" O. U N1 Al Cu Ti Method 'Ttgmop l min. 2 min. 2% min. 5-6 min.

30 14" 7. 5, s. 5 5 1 s40 r 4, 070, 000 3, 600,000 30 14 7. 5 3. 5 5' II 840 4. 800, 000 4, 600, 000 34' 14. 5. 7. 0 4. 5 5' I 84 5 4, 600. 000 4, 200, 000 3. 900, 000 y 3, 500, 000 34 14. 5 7. 0 4. 5 5 II 845 4, 900. 000 4, 900, 000 4, 800, 000 4, 700. 000 40, 14. 5 7. 6 4. 5 5 I 855 3, 600, 000 3, 000, 000 40. 14. 51 7. 6, 4. 5 5. II 855 U0, 0,

From the foregoing table'it is apparent that the presence of the magnetic field during cooling from above 1200 C. to about 600 C. and during reheating to. said temperature below the Curie point results in anincrease in the (13H) of at least 700,000 gauss-oersted.

.While the invention has been described in connection withspecific examples and applications thereof, these examples are illustrative only, the'invention being defined in the claims appended hereto.

What is claimed is:

1. In the method ofmanufacturing a permanent anisotropic magnet, the steps of forming a body of a ferrous alloy containing about 15 to 42% of cobalt, about 10 to of nickel, about 6 to 10% of aluminium, about 2. to 8% of copper, about 4 to 10% titanium, and the balance principally iron, rapidly cooling said body from a temperature exceeding about 1200" C. to about 600 C. within about 1 to 10 minutes in the presence of a magnetic field, increasing the temperature of said body from 600 C. to a temperature of about 10 to 70 C. below the Curie point thereof while in the presence of the magnetic field, and maintainingsaid body at a tem perature within said latter range not varying more than 20 C. and in the presence of the magnetic field for about 2. to 30 minutes whereby an anisotropic magnet is obtained having a (BH) value which is at least 700,000 gauss-oersted greater than obtainable by cooling a like body in the absence of a magnetic field.

2. A permanent anisotropic magnetmade by the method of claim 1.

3. In the method of manufacturing a permanent anisotropic magnet, the steps of forming a body of a ferrous, alloy containing about. 28 to 42% of cobalt, about 10 to 20% of nickel, about 6 to 10% of aluminium,

about 2to 8% of copper, about 4 to 10% titanium, and the balance principally iron, rapidly cooling said body from a temperature exceeding about 1200 C. to about 600 C. within about 1 to 10 minutes in the presence of a magnetic field, increasing the temperature of said body from 600 C. to a temperature of about 10 to C. below the Curie point thereof while in the presence of the magnetic field, and maintaining said body at a temperature within said latter range not varying more than 20 C. and in the presence of the magnetic field for about 2 to 30 minutes whereby an anisotropic magnet is obtained having a (BI-I) value which is at least 700,000 gauss-oersted greater than that obtainable by cooling 3. like body in the absence of a magnetic field.

4. In the method of manufacturing a permanent anisotropic magnet, the steps of forming a body Of afer! rous alloy containing about 15 to 42% of cobalt, about 10 to 20% of nickel, about 6 to 10% of aluminum, about 2 to 8% of copper, about 4 to 10% of titanium, and the balance principally iron, cooling said body from a temperature exceeding about 1200 C. to room tem-v perature while efiecting the cooling to about 600 C. within about 1 to 10 minutes in the presence of a magnetic field, heating said body to a temperature lying within a range of about 10 to 70 C. below the Curie point thereof while applying a magnetic field at temperatures above about 600 C., and maintaining said body for about 2 to 30 minutes in said magnetic field and at a temperature lying within said range and constant within about 20 C. to thereby obtain an anisotropic magnet having a (BH) value which is at least 700,000 gaussoersted greater than that obtainable by cooling. at like body in the absence of a magnetic field.

References Cited in the file of this patent FOREIGN PATENTS V 7 70,424 Netherlands July 15, 19,52 

1. IN THE METHOD OF MANUFACTURING A PEMANENT ANISOTROPIC MAGNET, THE STEPS OF FORMING A BODY OF A FERROUS ALLOY CONTAINING ABOUT 15 TO 42% OF COBALT, ABOUT 1O TO 20% OF NICKEL, ABOUT 6 TO 10% IF ALUMINUM, ABOUT 2 TO 8% OF COPPER, ABOUT 4 TO 10% TITANIUM, AND THE BALANCE PRINCIPALLY IRON, RAPIDLY COOLING SAID BODY FROM A TEMPERATURE EXCEEDING ABOUT 1200*C. TO ABOUT 600*C. WITHIN ABOUT 1 TO 10 MINUTES IN THE PRESENCE OF A MAGNETIC FIELD, INCREASING THE TEMPERATURE OF SAID BODY FROM 600*C. TO A TEMPERATURE OF ABOUT 10 TO 70*C. BELOW THE CURIE POINT THEREOF WHILE IN THE PRESENCE OF THE MAGNETIC FIELD, AND MAINTAINING SAID BODY AT A TEMPERATURE WITHIN SAID LATTER RANGE NOT VARYING MORE THAN 20*C. AND IN THE PRESENCE OF THE MAGNETIC FIELD FOR ABOUT 2 TO 30 MINUTES WHEREBY AN ANISOTROPIC MAGNET IS OBTAINED HAVING A (BH) MAX VALUE WHICH IS AT LEAST 700,000 GAUSS-OERSTED GREATER THAN OBTAINABLE BY COOLING A LIKE BODY IN THE BASENCE OF A MAGNETIC FIELD. 